Accordingly, as part of the Uganda Russia Boston Alcohol Network for Alcohol Research Collaboration on HIV/AIDS (URBAN ARCH) Consortium, we seek to expand and continue a cohort of HIV-infected adults to establish the Boston ARCH Cohort of 250 HIV-infected adults affected by multiple substances and that have a spectrum of alcohol use. This observational prospective cohort study will involve in-person assessments that will take place at 6-month intervals; participants will be followed for a minimum of 1 year and a maximum of 3.5 years. All assessments will include a researcher-administered questionnaire and breath alcohol test. In addition, the baseline assessment and each annual assessment (12, 24 or 36 months after enrollment) will also include: a urine pregnancy test (females only), blood collection, measurement of bone mineral density of the hip and spine (using Hologic QDR 4500W enhanced-array, whole-body, dual-energy radiographic absorptiometry [Bone Densitometer]), and measurement of bone microarchitecture of the wrist and ankle (using Xtreme CT [a device that measures high-resolution three-dimensional peripheral quantitative computed tomography]). We will conduct laboratory tests on blood samples collected at these time points, including tests for 25(OH) vitamin D3 and phosphatidylethanol (PEth). Remaining plasma and serum samples will be stored for future study of bone markers such as: parathyroid hormone, testosterone, carboxy-terminal collagen crosslinks (CTX) (a marker of osteoclast activity), and osteocalcin (osteoblast activity).